QTL Mapping of Wheat (Triticum aestivum L.) in Response to Salt Stress

Molecular markers provide a rapid approach to breeding for desired traits. To use them, it is necessary to determine the linkage between quantitative trait loci (QTL) and such markers. This study was conducted to investigate the genetic basis of salinity responses in Egyptian bread wheat (Triticum aestivum L.). In this context, a doubled haploid (DH) population (SGDH) of 139 individuals was produced from the cross between two Egyptian breeding cultivars (Sakha 93, salt tolerant) and (Gemmeza 7, salt susceptible). The DH population was tested under saline hydroponics culture and various plant responses were measured. A molecular genetic map of the SGDH population covering 3645.3 cM, was constructed using Restriction Fragment Length Polymorphism (RFLP), Microsatellite or Simple Sequence Repeats (SSR), and Amplified Fragment Length Polymorphism (AFLP) markers. In total, 325 loci along the 21 wheat chromosomes were mapped. The B genome showed the highest number of mapped markers followed by the A and the D genomes respectively. Interval and composite interval mapping (using QTL cartographer) were used to identify the genomic regions controlling traits related to salt tolerance with a threshold of LOD 3. Analysis of QTLs has revealed the approximate location of the significant markers associated with 12 traits related to salt tolerance traits across the A, B and D genomes. Fifty five significant QTL were detected on 15 of the 21 chromosomes mapped in this study, for some of these more than one QTL was identified. In many cases QTL were mapped very close to each other, indicating possible gene clustering or pleiotropy. For some traits, the total percentage of phenotypic variation explained by all QTL exceeded 50-60% but on average it was in the region of 15%. Chromosomes of homologues groups 2 and 5 exerted the biggest effect on most phenotypic traits, especially chromosomes 2B and 5B. The results indicated that there is considerable potential for improving salt tolerance of hexaploid wheat by using marker-assisted selection.